The most unique and promising aspect of ECT (emission computed tomography) techniques, which include both PET (positron CT) and SPECT (single photon ECT), is their potential to quantify regional cell functions through non- invasive imaging of 3D tracer distribution. This potential has already been partially realized in PET imaging, but it is much less well developed for the more popular and widely accessible SPECT because of the characteristic low efficiency, poor spatial resolution, and more severe attenuation effect. Although the inherent difficulty is greater, we are convinced that SPECT can be developed for quantitative imaging to a clinically meaningful level by further optimizing technical aspects of the imaging process. During the current project, we have successfully developed the first prototype brain SPECT system (McI) and are finishing a more practical clinical brain system (McII) with improved performance. As a direct extension of our existing project, this proposed project is to apply our concepts and expertise further along the same line to develop a body SPECT system. The general thrust of the project will remain unchanged: to optimize SPECT techniques through an integrated hardware and software approach. We will still place major emphasis on optimizing the front-end hardware to assure the quality of acquired data. Advanced processing techniques will be developed to optimally extract diagnostic information. The theme of this proposal is to develop a new high-performance SPECT system (McB) for cardiac imaging, while maintaining the potential for other body imaging applications. The development of a practical attenuation correction technique is crucial; this is a key for improving the quantification capability of the new imaging system. We have recently developed a novel concept which is implemented as a practical transmission imaging (AsFTCT) for deriving mu-maps, which are the pre-requisite for proper attenuation correction. We will integrated the new technique into the design of the proposed McB system. The design and construction of the McB system will improve the state-of- the-art of body and cardiac SPECT imaging. The high performance (sensitivity and/or high spatial resolution) and the quantification capability of the proposed system could lead to improved clinical utility of cardiac imaging. Equally significant, the proposed attenuation correction techniques developed are generic and applicable to other SPECT systems. This research project should contribute broadly to the advancement of SPECT imaging toward the long-term goal of quantitative functional imaging.